Use of sulphoxylates for stripping dyes



Patented Dec. 18,- 1928.

UNITED STATES PATENT OFFICE.

CHARLES S. HOLLANDER, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOB TO ROHM & HAAS COMPANY, A CORPORATION OF DELAWARE.

USE OF SULPHOXYLATES FOR STRIPPING DYES.

No Drawing.

The use of sodium sulphoxylate formaldehyde has been suggested as a desirable agent for stripping dyes from animal and vegetable fibres, due to its relatively low cost, its solubility in water and the fact that it need not be used in an alkaline solution (as in the case of sodium hydrosulphite for example) which would have an injurious effect on animal fibres. However, experience has shown that this substance has a tendency to break down too rapidly and deposit sulphur on the goods, which seriously interferes with subsequent dyeing operations.

The present invention relates to a method whereby sodium sulphoxylate formaldehyde can be used advantageously, and is. based upon my discovery that if the sodium salt is combined with a water-soluble salt of zinc, the sodium salt will be stabilized and give very efficient results. Zinc salts that may be used for this purpose include zinc sulphate, zinc chloride, zinc acetate or other salts of a similar nature. Inasmuch as it is desirable to add more or less acid to the stripping bath, some or all of the zinc may be added in a form which will combine with such acid to form a soluble zinc salt. For example, zinc oxide and sulphuric or acetic acid may be added instead of zinc sulphate or zinc acetate. However, in this case, as in the other, the bath will comprise a solution of sodium formaldehyde sulphoxylate mixed with a soluble zinc salt.

In this case, as in my earlier Patent No. 1,594,670, dated August 8, 1926, an equilib rium is established, but whereas in the former case the equilibrium involved some insoluble ingredients, in the present case all of the essential ingredients are soluble, for zinc hydroxide is not necessarily present as before and the soluble normal zinc sulphoxylate formaldehyle is present instead of the substantially insoluble basic compound, as shown by the following formula:

While the amount of zinc used may be varied within substantial limits, I find that efficient results can be obtained by using about half as much of the zinc salt as oft-he sulphoxylate; for example, 70% of sodium formaldehyde sulphoxylate and 30% of anhydrous zinc sulphate will give good results.

Application filed February 5, 1927. Serial No. 166,272.

The following is an example of my process':

Rags were first boiled with enough water to cover them, to which had been added about 5% of ammonia. This operation removed the dirt and grease and also extracted a considerable amount of dye. The goods were then thoroughly rinsed and heated to between 120 and 140 F. with enough water thoroughly to cover them. Between and 1% of acid (such as sulphuric, acetic, or formic) was: added and thoroughly mixed in and then 5% of a mixture of 70% sodium formaldehyde sulphoxylate with 30% of anhydrous zinc sulphate was introduced, and the water was heated until a temperature of between 190 and 200 F. was reached} After the goods had been heated for some time in this bath the dyes were found to be destroyed; the liquor was discarded and the goods thoroughly rinsed.

For the purposes of, convenience, the sodium formaldehyde sulphoxylate and the zincv salt may be prepared in dry powdered form and mixed to ether in the proper proportions and store or sold mixed to ether. They are then immediately available or use in preparing an efiicient stripping bath.

What I claim is:

1. The process of stripping dyes from fibres which comprises the step of soaking such fibres in a heated bath comprising dissolved substances in equilibrium, such substances comprising sodium sulphoxylate formaldehyde and a soluble zinc salt on the one hand and soluble zinc sulphoxylate formaldehyde and a soluble sodium salt on the other hand.

2. The method of preparing a bath for stripping d es from fibres which comprises the steps of dissolving together sodium sulphoxylate formaldehyde and a soluble zinc salt whereby an equllibrium of soluble ingredients is obtained comprising sodium Sillphoxylate formaldehyde and zinc sulphoxylate formaldehyde.

3. A composition of matter adapted for use in the production of a bath for stripping dyes comprising sodium sulphoxylate formaldehyde and a substantial amount of a soluble zinc salt, mixed together in powdered form, and adapted when dissolved in water to form a bath comprising dissolved substances in equilibrium, such substances comprising sodium sulphoxylate formaldehyde and a soluble zinc salt on the one hand and soluble zinc sulphoxylate formaldehyde and a soluble sodium salt on the other hand.

4. A composition as specified in claim.3 in which the amount of soluble zinc salt ,is 10 about half of the amount of sodium formaldehyde sulphoxylate.

CHARLES S. HOLLANDER. 

